The effect of aging on peptidergic neurons and monamine neurotransmitter systems will be determined in the monkey and rat brain. Quantitative microspectrofluorometric analysis of monoamine histofluorescence will be used to determine the relative intraneuronal content in the aged and young monkey and rat. Alternate section immunocytochemistry of neurophysin will be performed in order to determine the relationship during senescence between this peptide and monoamines which may influence the activity of vasopressin-and oxytocin-synthesizing neurons. Similar analyses will be performed for other peptidergic neuron systems such as gonadotropin-releasing hormone (GnRH) and somatostatin. This project will result in the depiction of brain monamine and neuropeptide systems in the aged animal in order to provide for a better understanding of altered function of these systems in the elderly.